The disclosure of Japanese Patent Application No. 2002-134642 filed on May 9, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a control apparatus for controlling an energy converter, such as electric motors that covert electric energy into kinetic energy, including rotary motors whose movable element is a rotor that undergoes rotational motion, and linear motors whose movable element is a slider that undergoes linear motion, or generators that convert kinetic energy into electric energy by rotating or moving a movable element, and also relates to a control method thereof.
2. Description of the Related Art
FIG. 10 illustrates the principle of a two-pole alternating-current motor (synchronous motor). This drawing schematically illustrates a revolving-field type motor in which an armature winding is provided on a stationary element (stator), and a field winding is provided on a movable element (rotor). The electric motor having this structure is termed revolving-field type motor. In contrast, an electric motor having a structure in which a field winding is provided on the stationary element side and an armature winding is provided on the rotor side is termed revolving-armature type motor. In general, the revolving-field type motors are simpler in structure than the revolving-armature type motors, and the revolving-field type motors require lower field voltage and current than the revolving-armature type motors. Therefore, the revolving-field type motors are more often employed. When the field winding provided on the rotor is excited, the rotor becomes an electric magnet, and rotates synchronously with revolving magnetic fields produced by three-phase alternating currents supplied to the stationary element side.
A three-phase brushless motor which is a permanent magnet-type synchronous motor is described in Japanese Patent Application Laid-Open Publication No. 9-47066.
FIG. 11 is a block diagram of a brushless motor 4 similar to the brushless motor described in Japanese Patent Application Laid-Open Publication No. 9-47066. An alternating-current signal voltage output from an alternating-current oscillator 1 is converted into a direct-current bias voltage by an AC/DC converter portion 2, and is supplied to an inverter circuit 3. The inverter circuit 3 is driven by a control signal output from a drive circuit 7 so as to generate a three-phase alternating-current voltage from the direct-current bias voltage.
The inverter circuit 3 has three transistor arrays that are provided in parallel between direct-current bias voltages. A first transistor array is made up of a transistor Ua, and a transistor X that are connected in series. A second transistor array is made up of a transistor Va and a transistor Y that are connected in series. A third transistor array is made up of a transistor Wa and a transistor Z that are connected in series. A diode is connected between the emitter and the collector of each transistor, thus allowing passage of current only in one direction. If the transistors are field-effect transistors, a diode is connected between the source and the drain of each transistor.
If current is allowed to flow by turning on the downstream-side transistor while maintaining the off state of the upstream-side transistor of an array, the electric potential at a boundary node between the upstream and downstream-side transistors drops. In the case of the converse on/off states, the potential rises. In this manner, the boundary node potential in a transistor array can be raised and dropped by switching the transistors via a drive circuit 7. By shifting the alternating currents caused by variations of the boundary node potentials occurring in the first, second and third transistor arrays by 120 degrees in phase, three-phase alternating current can be generated. A command for the transistor switching for the purpose of generating three-phase alternating current is output from a control circuit 6.
If three-phase alternating current is randomly supplied to armature windings U, V, W, the motor becomes out of synchronization. Therefore, three-phase alternating current is supplied synchronously with the present position of a movable element of the motor. If the phase of three-phase alternating current is adjusted by detecting the position of the movable element, a feedback control can be realized by detecting the position of the movable element and adjusting the phase of three-phase alternating current based on that detected position. If the phase of three-phase alternating current is adjusted on the basis of the position of the movable element that is expected upon supply of the three-phase alternating current, an open-loop control can be performed. In order to perform the open-loop control, it is necessary to detect the phase of three-phase alternating current. In the example shown in FIG. 11, therefore, a position detector circuit 5 is connected to the three armature windings.
In conjunction with a control apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 9-47066, a method for detecting the mounting error of a magnetic pole position sensor in order to accurately determine the position of the movable element is disclosed. In this method, the inverter circuit is opened, and an induced voltage is measured. Then, a mounting error is detected by comparing the induced voltage with an output of the magnetic pole position sensor. Since such an error incurs a reduction in driving efficiency, it is preferable that the error be minimized.
However, a problem of the aforementioned control apparatus is that unless many special circuits are used, sufficient error detection cannot be achieved.
It is an object of the invention to provide energy converter control apparatus and method capable of measuring an error regarding the position of a movable element while employing a simple construction.
A first aspect of the invention relates to an energy converter control apparatus for controlling an energy converter which has a movable element that has a field winding, and a stationary element that has an armature winding, and which is able to move the movable element by supplying an alternating current to the armature winding while supplying a current to the field winding. During a state where supply of the alternating current to the armature winding is suspended, the energy converter control apparatus moves the movable element while the field winding is supplied with a current that is at most a predetermined value, and measure an induced voltage induced in the armature winding. Since the induced voltage corresponds to the position of the movable element, it is possible to determine the position of the movable element from the induced voltage.
A second aspect of the invention relates to an energy converter control apparatus for controlling an energy converter which has a movable element, and a stationary element that has a plurality of armature windings, and which is able to move the movable element by supplying a multi-phase alternating current to the armature windings. The apparatus supplies a current to the armature windings so that the current through the armature windings becomes zero while the movable element is moving, and measures a voltage of the armature windings.
In this case, the voltage of the armature windings changes in accordance with the position of the movable element. Since the voltage of the armature windings corresponds to the position of the movable element, it is possible to determine the position of the movable element from the voltage of the armature windings.
A third aspect of the invention relates to a method for controlling an energy converter which has a movable element that has a field winding, and a stationary element that has an armature winding. The method includes the steps of: supplying the field winding with a current that is at most a predetermined value and that is able to move the movable element during a state where supply of the alternating current to the armature winding is suspended; and measuring an induced voltage induced in the armature winding while the current is supplied to the field winding.
In this method, as a current that is at most a predetermined value and that is able to move the movable element, a level of current that does not cause power generation is supplied to the field winding. At this time, an induced voltage induced in the armature winding is measured. As in the first aspect of the invention, it is possible to determine a position of the movable element from the measured induced voltage.
The fourth aspect of the invention relates to a method for controlling an energy converter which has a movable element, and a stationary element that has a plurality of armature windings. The method includes the steps of: supplying a current to the armature windings so that the current through the armature windings becomes zero during a state where the movable element is moving; and measuring a voltage of the armature windings while the armature windings are supplied with the current.
Since the voltage of the armature windings changes in accordance with the position of the movable element, this method allows the position of the movable element to be determined from the measured voltage of the armature windings as in the second aspect of the invention.